Sound reproducing apparatus



Dec. 1, 1942. R vQ SANDER$ JR 2,304,022

SOUND REPRODUCING APPARATUS Filed Nov. 30, 1940 '2 Sheets-Sheet l Dec. 1, 1'942.

R. c. SANDERS, JR 2,304,022 SOUND REPRODUCING APPARATUS 2 Sheets-Sheet 2 Filed Nov. 30, 1940 Patented Dec. 1, 1942 2,304,022 I SOUND REPRODUCING} APPARATUS Royden C. Sanders, Jr., Audubon, N. .I., assignor to Radio Corporation of America, a corporation of Delaware Application November 30, 1940, Serial No. 387,889

9 Claims.

This invention relates to sound reproducing apparatus, and more particularly to loudspeakers, the primary object of my invention being to provide a novel loudspeaker for converting electrical energy into acoustical energy and in which the power which generates the sound is not taken, to any appreciable extent, from the electrical input to the vibrating parts thereof.

More particularly, it is .an object of my invention to provide a novel loudspeaker in which the electrical input controls the 'sound output insomewhat the same way that the grid electrode of an electron discharge device controls the plate current.

Another object of my invention is to provide a novel loudspeaker as aforesaid wherein a much smaller vibrating element is required, for a given power output at a given low frequency, and with less electrical audio input power, than is required with conventional loudspeakers.

A further object of my present invention is to provide a novel loudspeaker as aforesaid which has relatively small baille requirements.

Still a further object of my invention is to provide a novel loudspeaker which has greatly improved transient response over conventional loudspeakers. I

It is also an object of my invention to provide a novel electro-mechanical loudspeaker in connection with which high power audio amplifiers will not be required. a

Another object of my invention is to provide a novel loudspeaker as aforesaid which has a uniform frequency response.

Still another object of my invention is to provide a novel loudspeaker as set forth above which is capable of reproducing sound with high fidelity. I

A further object of my invention is to provide a novel loudspeaker which is fairly simple in construction, highly efficient in use, and of relatively small cost, particularly when considered from the standpoint of economy of operation and eiiiciency.

The novel speaker constituting my present invention may be designated as a "fan type loudspeaker, and its construction and operation, according to one form thereof, is as follows: A set of peripherally mounted blades is carried by a suitable suspension and rotated at a very high speed by a conventional electric motor. The blades are so mounted that they are adjustable in pitch but will generate no torque about their respective axes regardless of the angle at which the blades are set. The amount of air that the I teristic of my invention fan blades push forward or pull backward will,

of course, depend upon the instantaneous pitch of the blades. Coupled to the blades for altering their pitch in accordance with signal energy is an, electro-mechanical driver, the pitch or angle of attack of the blades being determined by the instantaneous voltage applied to the driver.

Since the instantaneous sound pressure generated by the blades varies as the instantaneous pitch thereof, it follows that a sound corresponding to the applied audio voltage will be generated by the blades.

The blades are preferably made of some suitable flexible, resilient material and are arranged circularly about a common axis, each blade being mounted for twisting movement out of its plane on a radial axis, so that its pitch can be varied. As noted heretofore, their. axes are so chosen and the blades are so designed that no torque is generated about their respective axes at any pitch of the blades and even at full speed rotation of the fan. Thus, it is apparent that the unit may be so designed that the instantaneous pressure developed is directly proportional to the instan-' mechanical driver. It isalso apparent that the acoustical power generated will come mainly from the power developed by the electric motor which rotates the fan unit, and the portion of the acoustical power converted from the electrical audio input is very inappreciable. As a matter of fact, the workwhich the audio electrical power must do is mainly in overcoming the small amount of residual radiation resistance present even when the blades are not rotating plus the loss in the electrical driving circuit necessary in supplying the required power at poor power factors. The efiect of reflected sound, such as may be obtained from trapping the backward radiation, is inappreciable upon the electrical input circuit or upon the position of the blades on their radial axes, and as a result of this, much smaller bailies may be used with my novel loudspeaker than has been required heretofore with conventional speakers.

The novel features that I consider characare set forth with particularity in the appended claims. 7 The invention. itself, however, both as to its organization and method of operation, objects and advantages thereof, will best be understood from the following description of several embodiments thereof, when read in connection with the accompanying drawings in which Figure 1 is a side elevation, partly'in section,

as well as additional a l showing one form of loudspeaker constructed in a my present invention,

myinvention,

fragmentary view similar to'Fig.

secured a s'pider-like-cage so that the cage 1 relatively high speed.

'- of annular clamping vibration,.

mm. a a

J flexible, resilient material,

- out. from the sheet in correspond in number to tially spaced the same angle as the tails 2| and tro-mechanicai accordance with my present invention,

Figure 2 is a front elevation of one diaphragm and mounting therefor according to Figures 3, 4 and 5 are fragmentary views similar to Fig. 1 showing other s efi e 4 1 showing another form of" loudspeaker employthe principle of my present invention,

Figure 7: is a fragmentary showing a portion of the diaphragm and blades thereof employed in' the-loudspeaker of Fig-6,. and

Figures 8 and 9 are fragmentary front elevational views of a diaphragm somewhat ,similar to but employing different.

that shown. inFig. 2 blade mountings- I Referring more particularly" to the drawin wherein similar reference 'characters designate corresponding parts throughout, thereis shown, in Fig, l, a more or tor l to the casing of cage or drum 3 and of wire or the like -1,

The cage I carries a pair rin s I between which a 'vibratible unit is clamped and supported for the clamping rings 8 being provided with a plurality of inwardly directed, radially extending and eircumferentially spaced saw-tooth,

presently to be 'setprojections II for a p'm'poee The vibratible mem l I, as shown more clearly in Fig. 2, is preferably made of relatively thin,

num, paper. paper pulp, synthetic resin. or' the like, in sheet form and may be stamped or out which slots the sheet central huh I! along the radially outwardly from a slots ii to provide a plushaped blades l'l. The cutting die preferably also removes portions I! from adjacent the periphery of'the sheet to provide the radially extending tails If at the outer ends of the blades 11. .The saw-tooth projection ii on the clamping rings 8 and are circumferenserve to clamp the tails 2| therebetweem It will be obvious, therefore, that displacement of the hub I! along the axis of the rotor 5 fromthe position which thehub is normally occupies at rest will cause the blades 2! to twist out of their common plane along radial axes passing through the centers ofthe tails II by 'reason'of the fact that the inclined edges of the saw-teeth 13 extend across the radial axes passing through the tails 2! at anangle thereto. Movementof the hub Ii to the right, as seen in Fig. 1, will cause the blades II to twist in one directionfand movement of the hub "to the left. as seen in Fig. l, i

will cause the blades direction. a

For eifectin displacement of the hub Is, there may be'mounied on the drum 3 any suitable elecdri'ver, such as the electrodynamic unit constituted by the field structure 23 and the voice coil 25 carried on a spider 21, the spider I], also having secured thereto an open-ended cap member 2! which a hollow cap 3| secured I! to twist lnthe opposite to thehub IS, the loose nt the cap member as around the cap 3| proform of modifications, of

front elevation less conventional electric mowhich is fixed a stationary to the rotor I of. which is I rotates with the rotor at a fits loosely over and around.

a placement at Fig. 3 illustrates a constructionsimilar to that instead of employing the and it is for this reason that the such as mica, alumionepiece by a suitable die rality of discrete, substantially contiguous, wedge- 5, the gage -'l and-the hub all being secured,

' the driver 43 and the h the driver 43 rotates with the rotor 5, the drum ing the driver on cylindrical portions of' leads to the driver this modification,

air space it between the the two caps (exaggerated viding a thinannular in the drawings as to clearness) and a' fluidcolumn 35 between the endsfthereoi. when signal voltages within the audio frequency range are applied to the voice coil 25, the cap member 2'! is displaced from its normal positionvand, through the column of air 3i and the hub II.

in the space 3!, drives This causes the blades while the member ll speed by the motor I and, in turn, eflects air disacoustical frequencies;

the cap H to twist correspondingly shown in 1, but electrodynamic driver 2P2, an electro-magnetic driver 31 may be mounted on the drum 3 for cooperation with a soft iron armature ll so cured to the hub ll. Signal voltageslapplied to the coils 41 of the driver 31 will cause the as- -.sociated cores to more the drivers of 'these'mod is of the diaphragm II,

and 35 are provided in the modification of Fig. l and the air gap between magnets and the armatures may be desired some cases, it to provide a rigid coupling between the driver and the diaphragm H, and in such cases, it ,is necessary that the driver shall rotate of any suitable type, eiectrodynamic, condenser, piezoelectric crystal driver, or. the like, is formed with a hub I by means of which it is secured to the rotor 5, the

cage 1 being fitted over the hub 45, and the rotor together for rotation as a unit.. A rigid coupling,

such as a driving rod 41, may be suitably secured to the vibratible member ii at the hub portion is thereof to effect'the desired coupling between vibratible member. Since I may be entirely eliminated. To provide input 43, the rotor 6 may be made hollow and the input leads I! brought in through the rotor. v Where practical considerations dictate mount the stationary frame or drum 3 ends rigid coupling is desired between the driver and the member H, a construction such as that shown in Fig. 5 may be employed. In the driver 43 is mounted on the drum 3, as in the modifications of Figs. 1 and 3, and the hub portion provided with a small opening ll. The coupling rod 41 between the driver 43 and i5 is provided with a Jewel-bearing member I: 1

5|. On the other side the hub portion which fits into the opening of the member II, the rotor I is formed with a reduced end in. and axially aligned with the rotor portion 5a is a pin 55 which also carries a jewel bearing 51 fitted into the opening I. A coil thickness for the sake of is being rotated at a high hub II and corresponding the blades H on their and 3, the drivit is necessary to provide a air spaces on the cores of the electro- 30 are provided in the form oi my invention shown in Fig, 3. In

p with the diaphragm. A com struction which operates in this manner is shown 'in Fig.4 wherein the driver 43, which may be such as an electromagnetic,:

15 of the diaphragm II is the pin 55 and serves to press the bearing 51 against the hub portion l and the latter against the bearing 53. A space 8| is, of course, provided between the ends of the rotor portion 5a and the pin 65 to permit vibration of the diaphragm ll in response to the signal-voltages appliedto the driver 43. a v

In the modifications of my invention thus far described, use is made of mechanical means to p eifect vibration or twisting of the blades II. An-

other method of changing the angle of the fan blades H with the applied signal 'voltagdla-shown in the modification mustratedmmie. In this modification, the cage 1 is omitted and the hub 15 of the member H is secured to the rotor 5,- the clamping rings 8 being secured to the tails 2| of the fan blades". One-half of eacheof the blades i1. is coated with a conducting material 63, as clearly shown in Fig. 7, the material 631 being applied by spraying or in any other suitable manner, and the conducting material 63 conthe many advantages heretofore set forth. As

'shown in Fig. 2, the vibratible member II is formed with sixteen blades. However, it will be apparent that any number of blades may be employed. In designing the vibratible member and the mounting therefor, it should be kept in mind that the resonant freguencyof the vibrating system is determined to a large extent by -(1) the rotational inertia of the individual blades l1, (2) the mass of the center clamping members, such as the discs 89, and (3) the stiffness presented by the blade suspensions at the tails 2| and am. In general, it may bestated that the use of as many fan blades as possible is desirable.

tacting the clamping members 8 and being conneoted thereby to ground, as by means of one or more conductors 64 connecting the members 9 to the grounded rotor 5. The conductors 84 are preferably uniformly distributed circumferential- 'Also,-the blades should preferably bemade of the lighstand strongest materials possible. Although I-have shown and described a number of modifications of my invention. it will be apparent to those skilled in the arm-that many other modifications, as well as changes in those described, are possible. I therefore desire that my invention shall not be limited except insofar as is made, necessary by the prior art and by the spirit of the appended claims.

I claim as my invention:

1. In a sound translating device, the combination of a rotatable member, means for rotating ly about the rings 8 and pass radially outwardly from the-rotor 5 to the rings 9 over suitable ones of the slots IS in the member if, was not-to interfere with the vibration of the blades H. For

my invention, may be made somewhat wider than in the other modifications. The blades in this modification are twisted or deflected about their respective axes by an electrostatic force obtained from a pair of fine mesh wire screens 65 carried on the drum 3 on each side of the member ll and to'which the audio driving signals are applied through a step-up transformer 86. The screens 65 are supplied with a suitable polarizing potential by means of a battery 68 connected between the mid-tap of the secondary winding of g the transformer 66 and .the drum 3 whichis In Figs. 8 and 9, there are shown modified forms of fan blade assemblies. Instead of-stamping the assembly out of a single sheet member I I, as described above, the substantially wedge-shaped blades l1 maybe individually stamped out and provided with a tail-at each end. The outer tails 21 are clamped, as before, between the saw-tooth projections it of the clamping rings 9, and the this purpose, the slots Ii, in this modification or I v to said unit for rotating said unit, means mountinner tails 2 la are clamped between the saw-tooth projections '61 of a pair of discs 59 which take the place of the hub portion ii in the modifications previously described. The angular edges of the saw teeth i3 and 61 may be made parallel to each other, as shown in Fig. 8, or they may be angularly related as shown in Fig.9. In any case, upon displacing the discs 69 from their normal, rest position, it will be obvious that the blades 21 will be twisted in the manner described above.

From the foregoing description, it will be apparent to those skilled in the art that I have provided an entirely novel loudspeaker which has said member on a predetermined axis,.and means for simultaneouslyvariably rotating said member about another axis angularly related to said first named axis and at frequencies within the audible range. p 2. In a sound translating device, the combination'of a vibratible member, means for rotating said member about apredetermined axis, and means for oscillatably twisting said member about an axis substantially normal to said first named axis and at frequencies within the audible range.

3. In a sound translating device the combination of a vibratible member comprising, as a unit, a hub and a plurality of discrete blades extending radially with respect to and spaced circumierentially about said hub, a motorfcoupled ing each of said blades for twisting movement thereof about an axis in the plane thereof, said blade axes also being radially related to said hub, and a second motor responsive to audiofrequency impulses coupled to'said unit for twisting said blades about their respective axes whereby'to vary the pitch of said-blades relative to said hub at audio frequencies.

4. Ina sound translating device, the combination of a vibratible member comprising, as a unit, a hub and a plurality of discrete blades extending radially from and spaced circumferentially about said hub, a motor coupled to said unit for rotating said unit, means mounting each of said blades for twisting movement thereof about an axis in the plane thereof upon displacement of said hub from its normal position, said blade axes also being radially related to said hub, and a second motor responsive to audiofrequency impulses coupled to said hub for displacing said hub from its normal position at frequencies within the audio spectrum whereby to correspondingly twist said blades about their respective axes and thereby correspondingly varying the pitch of said blades relative to said hub.

v5. The invention set forth in claim 4 characterized in that said hub and said blades are constituted by an integral'piece of flexible and resilient sheet material slotted radially from said hub at a plurality of circumferentially spaced points.

6. The invention set forth in claim 4 characterized in that each of said blades terminates in a relatively narrow tail along the axis of the blade, and characterized further in that said mounting means is constituted by a pair of clamping members having a plurality of cooperating saw-tooth projections thereon between which said tails are clamped, said saw-tooth projections being angularly related to the axes of their respectively associated blades.

'7. The invention set forth in claim 4 characterized in that said mounting means includes a pair of cooperating clamping rings to which the marginal portions of said blades are secured, and characterized further in that said first named motor includes a rotor element coupled to said clamping rings.

, 8. The method of efiecting air displacements within the audio frequency range which comprises rotating a member on a predetermined axis,

and simultaneously variably rotating said member at audio frequencies about a second axis normal to said first named axis.

9. In signal translating apparatus, the combination of a diaphragm comprising a normally plane member having a hub portion and a plurality of substantially wedge-shaped portions extending radially outwardly from said hub portion, said wedge-shaped portions being slightly spaced from ,each other in a direction circumferentially around said hub portion and being movable relative to said hub portion, each of said wedge-shaped portions having an extension thereon extending radially outwardly from its periphery, and clamping means including elements engaging said extensions and confining movement of said wedge-shaped portions to 1'0- tation each on a radial axis passing through its extension.

ROYDEN-C. SANDERS, JR. 

